3GPP (3rd Generation Partnership Project) that is a standardization project of mobile communication systems is working on standardization of LTE Advanced that is an advanced version of LTE (Long Term Evolution) in 3GPP release-10 or later (see, for example, Non-Patent Document 1).
In LTE-Advanced, provision of a heterogeneous network is under study in which a low power base station (so-called pico base station and home base station) is installed in a coverage area of a high power base station (so-called macro base station). The heterogeneous network can distribute the load on the high power base station to the low power base station.
To achieve a wider band width while securing backward compatibility with LTE, a carrier aggregation technique is introduced in LTE Advanced. In the carrier aggregation technique, a carrier (frequency band) in LTE is regarded as a component carrier (CC), and multiple carriers are used in combination for radio communications.